Hitherto, solar modules often have not been equipped with special safety provisions. The solar connection box (also known as solar junction box) provided on each solar module is essentially used to accommodate the mechanical connections of the conductive strips (also known as conductor ribbons) of the solar module and the bypass diodes thereof. Such simple solar modules will supply voltage as soon as they are illuminated.
Typically, the solar modules are series-connected so as to form strings in order to obtain a high string voltage. This voltage of the solar modules connected into strings can amount to several 100 V, and in large systems voltages of about 1000 V or even more may be present, which is a hazardous voltages being touched. Also, a solar power system optionally comprises a plurality of strings connected in parallel.
Thus, in case of adequate illumination very high voltages might be generated during the installation of solar modules and when electrically connecting them in the string, so that cautious handling and a special contact protection is required. The same applies to maintenance works.
In such simple photovoltaic systems the first possibility for disconnecting the solar generator voltage from the power grid is at the string combiner box. Therefore, in case of damage caused by fire, water, hail or in case of other malfunctions of the solar modules or the string lines there is no way for these simple solar modules to de-energize or disconnect the part of the photovoltaic system that includes the solar modules and the string lines from voltage.
Safety devices for switching off the individual solar modules in case of fire or faults are known (e.g. DE 10 2009 024 516 A1). However, such solutions are usually only intended for a single emergency shutdown.
DE 10 2011 110 682 (not pre-published) discloses a junction box which switches from the operating state to a safe state in case of a deviation of the allowed parameters.
As an enhancement of the invention described in DE 10 2011 110 682, the present disclosure relates in particular to a controlled and safe initial connection or starting of a photovoltaic system using “smart” solar junction boxes and to a safe and controlled reconnection or restarting after a shutdown of the solar junction boxes, for example after incidents, maintenance work, or at sunrise. The content of DE 10 2011 110 682 is hereby fully incorporated by reference.
WO 2010/078303 describes a signal generator which continuously applies an RF enable signal to the positive and negative branch of a PV string. The disadvantage here is that the RF enable signal must be applied permanently to maintain the system in the operation state, and that the PV modules possibly will not provide electric power for components in the junction box or will require additional RF signal bypasses and do not ensure reliable prevention of open voltages. Furthermore, power loss or additional power consumption may be caused by the enable signal generator. In case of a malfunction of the RF enable signal, PV modules or even the entire PV string may be unnecessarily shut down, which may result in reduced power feed to the grid.